December 4, 2007—As the U.S. Library of Congress readies the first map to use the name "America" for its public debut, some researchers are wondering where in the world the mapmaker got his information.

The world map, created by German cartographer Martin Waldseemüller in 1507, is the first document to show a separate Western Hemisphere and label the Pacific Ocean as its own body of water.

Before he drew the document, Waldseemüller had pored over notes from explorers Christopher Columbus and Amerigo Vespucci, as well as other unknown Portuguese and Spanish sources, according to a statement from the Library of Congress.

"It represented a modern view of the world," the statement said.

But some scholars are confused as to how the mapmaker knew the Pacific Ocean existed years before explorers found it, and how he depicted South America so accurately.

"From the writings of Vespucci you couldn't have prepared [this] map," John Hebert, chief of the geography and map division at the library, told Reuters.

It's also unclear why Waldseemüller stopped using the name "America" in later maps, referring to the land only as "terra incognita," or "unknown land," Reuters reported.

The German scholar did mistakenly name the new lands America after Vespucci's first name, thinking he—not Columbus—had discovered them, according to the library.

Waldseemüller later had misgivings about the error, the Library of Congress's Hebert told the Reuters news service.

The map was rediscovered in 1901 after spending 400 years lost in the library of a German castle.